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United States Patent |
5,144,973
|
Green
,   et al.
|
September 8, 1992
|
Safety valve for compressed gas cylinders
Abstract
A safety valve for fitting into a compressed gas cylinder to terminate gas
flow from the cylinder when a primary gas valve attached to the cylinder
port of the cylinder is deflected or severed. The safety valve is
independently supported in the cylinder port below the location of the
primary gas valve. A threaded housing having a channel for the passage of
gas to and from the cylinder is threaded into the cylinder port below the
location of the primary gas valve. A poppet seat is provided in the
housing. A tubular portion of the threaded housing extends up and fits
snugly into the gas passage of the primary gas valve. A cylindrical
housing having apertures for the passage of gas is attached to the
threaded housing. A poppet is provided in the cylindrical housing, which
is biased into the poppet seat by a helical spring. The poppet is held off
of the poppet seat by means of a frangible element. A relatively minor
deflection, or shearing off, of the primary gas valve will be passed
through to the frangible element, resulting in the breaking of the element
and thereby allowing the poppet to seat in the poppet seat preventing the
flow of gas from the cylinder to the primary gas valve. A polymer collar
may be used in connection with the safety valve to eliminate thread
leakage. A remote triggering device is set forth for seating the poppet in
the poppet seat without a deflection or severing of the primary gas valve.
Further, a flow restriction device for use with the safety valve is
described.
Inventors:
|
Green; J. Kenneth (Ruidoso, NM);
Watson; Eugene L. (Placitas, NM);
Whalen; Paul S. (Oahu, NM)
|
Assignee:
|
Safety Assurance Corporation (Albuquerque, NM)
|
Appl. No.:
|
800046 |
Filed:
|
November 29, 1991 |
Current U.S. Class: |
137/71; 137/67; 137/68.11; 137/68.14; 137/76; 137/513.3; 137/910 |
Intern'l Class: |
F16K 017/40 |
Field of Search: |
137/68.1,71,76,513.3,855
|
References Cited
U.S. Patent Documents
2563244 | Aug., 1951 | Holiger | 137/71.
|
2945503 | Jul., 1960 | Atkinson | 137/68.
|
3618626 | Nov., 1971 | Russo | 137/68.
|
3630214 | Dec., 1971 | Levering | 137/68.
|
3645286 | Feb., 1972 | Follett | 137/68.
|
3648893 | Mar., 1972 | Whiting | 222/3.
|
3794057 | Feb., 1974 | Badger | 137/68.
|
3930517 | Jan., 1976 | Gagala | 137/71.
|
4064889 | Dec., 1977 | Gayle | 137/68.
|
4077422 | Mar., 1978 | Brinkley et al. | 137/68.
|
4562852 | Jan., 1986 | Britt | 137/68.
|
4907617 | Mar., 1990 | Whalen | 137/71.
|
Primary Examiner: Rivell; John
Attorney, Agent or Firm: Lansdowne; John R.
Claims
What is claimed is:
1. A safety valve for a compressed gas cylinder to terminate gas flow from
said cylinder when a primary gas valve attached to a cylinder port of said
cylinder is deflected or severed, said safety valve being independently
supported below said primary valve in said cylinder port, comprising:
a threaded housing having a channel for the passage of gas adapted to be
received in said cylinder port below said primary gas valve, a tubular
portion of said threaded housing extending into a gas passage of said
primary gas valve;
a cylindrical housing adapted to be received inside said cylinder and
attached to said threaded housing having an aperture for the passage of
gas from said cylinder to said threaded housing;
a poppet seat furnished in said threaded housing;
a poppet furnished in said cylindrical housing;
bias means furnished in said cylindrical housing to urge said poppet into
said poppet seat; and
a frangible element disposed in said threaded housing and holding said
poppet off said poppet seat against the urging of said bias means whereby
upon the severing or the deflection of said primary gas valve said
frangible element will break thereby allowing said poppet to seat in said
poppet seat and preventing the flow of gas from said cylinder to said
primary valve.
2. A safety valve as in claim 1, wherein a deflection of the primary gas
valve as much as 10 degrees from the normal will break said frangible
element.
3. A safety valve as in claim 1, wherein said bias means is a helical
spring.
4. A safety valve as in claim 1, further including a collar having inside
and outside threads adapted to be received in the cylinder port and to
accept said threaded housing so as to hold said safety valve in said
cylinder port.
5. A safety valve as in claim 4, wherein said collar is made from a polymer
material.
6. A safety valve as in claim 5, wherein said collar is made from a Kel-F.
7. A safety valve as in claim 1, wherein said frangible element has a high
ratio of compression and tensile strength to shear strength.
8. A safety valve as in claim 7, wherein said frangible element is a
ceramic material.
9. A safety valve as in claim 8, wherein said ceramic frangible element is
alumina.
10. A safety valve as in claim 7, wherein said ceramic frangible element is
in the shape of a pin.
11. A safety valve as in claim 10, wherein said ceramic frangible pin is
mechanically weakened to induce breakage at a predetermined zone.
12. A safety valve as in claim 11, wherein said ceramic frangible pin is
weakened by a waist cut round the pin.
13. A safety valve as in claim 11, wherein said ceramic frangible pin is
weakened by a series of circumferential holes ablated into the pin by use
of an industrial laser.
14. A safety valve as in claim 13, wherein said ceramic frangible pin is
weakened by 10 to 20 approximately equally spaced circumferential holes
with an aspect ratio of approximately 1:1 ablated into the pin by means of
an industrial laser.
15. A safety valve as in claim 1, further including insertion means to
thread said safety valve into said cylinder port whereby pivotal movement
of a tool engages said insertion means and seats said valve into said
cylinder port.
16. A safety valve as in claim 1, further including means to couple said
safety valve to said primary gas valve and mating means incorporated into
said primary gas valve whereby said safety valve and said primary gas
valve can be seated together into said cylinder port.
17. A safety valve as in claim 16, wherein said coupling means consists of
a slot in said threaded housing of said safety valve and a mating prong
protruding from the bottom of said primary gas valve.
18. A safety valve as in claim 1, further including remote actuation means
to achieve the seating of said poppet in said poppet seat without the
deflection or severing of said primary gas valve.
19. A safety valve as in claim 18, wherein said remote actuation means
consist of the use of a fusible material in said tubular portion of said
threaded housing to receive said frangible element and the heating of said
fusible material to a temperature above its melting point, whereby said
fusible material fails under the force exerted by said bias means and said
poppet seats in said poppet seat.
20. A safety valve as in claim further including flow restriction means to
regulate the flow of compressed gas from said cylinder while allowing the
unimpeded filling of said cylinder.
21. A safety device as in claim 20, wherein said flow restriction means
consists of a flap with an aperture therein pivotally attached to said
cylindrical housing, such that cylinder pressure forces said flap against
said cylindrical housing covering said aperture in said cylindrical
housing and allowing gas flow only through said aperture in said flap,
while the pressure of gas filling the cylinder forces said flap away from
said cylindrical housing allowing for the unimpeded filling of said
cylinder.
22. A safety valve for a compressed gas cylinder to terminate gas flow from
said cylinder when a primary gas valve attached to a cylinder port of said
cylinder is deflected or severed, said safety valve being independently
supported below said primary valve in said cylinder port, comprising:
a threaded housing having a channel for the passage of gas adapted to be
received in said cylinder port below said primary gas valve;
a frangible tube attached to said threaded housing and extending into a gas
passage of said primary gas valve;
a cylindrical housing adapted to be received inside said cylinder and
attached to said threaded housing having apertures for the passage of gas
from the cylinder to said threaded housing;
a poppet seat furnished in said threaded housing;
a poppet to cooperate with said poppet seat to terminate gas flow from the
cylinder;
a bias means furnished in said cylindrical housing to urge the said poppet
into the said poppet seat; and
means to oppose said poppet in said frangible tube whereby said poppet is
held off said poppet seat against the urging of said bias means whereby
upon the deflection or severing of the primary gas valve said frangible
tube will break thereby allowing said poppet to seat in said poppet seat
and preventing the flow of gas from said cylinder to said primary valve.
23. A safety valve as in claim 22, wherein a deflection of the primary gas
valve as much as 10 degrees from the normal will break said frangible
tube.
24. A safety valve as in claim 22, wherein said bias means is a helical
spring.
25. A safety valve as in claim 22, wherein said means to oppose poppet
consist of two opposing apertures cut through the walls of the frangible
tube and a spring pin received through said apertures.
26. A safety valve as in claim 22, further including a collar having inside
and outside threads adapted to be received in the cylinder port and to
accept said threaded housing so as to hold said safety valve in said
cylinder port.
27. A safety valve as in claim 26, wherein said collar is made from a
polymer material.
28. A safety valve as in claim 27, wherein said collar is made from Kel-F.
29. A safety valve as in claim 22, wherein said frangible tube has a high
ratio of compression and tensile strength to shear strength.
30. A safety valve as in claim 29, wherein said frangible tube is a ceramic
material.
31. A safety valve as in claim 30, wherein said frangible ceramic tube is
alumina.
32. A safety valve as in claim 30, wherein said ceramic frangible tube is
mechanically weakened to induce breakage at a predetermined zone.
33. A safety valve as in claim 32, wherein said ceramic frangible tube is
weakened by a waist cut round said tube.
34. A safety valve as in claim 32, wherein said ceramic frangible tube is
weakened by a series of circumferential holes ablated into the tube by use
of an industrial laser.
35. A safety valve as in claim 22, further including insertion means to
thread said safety valve into said cylinder port whereby pivotal movement
of a tool engages said insertion means and seats said valve into said
cylinder port.
36. A safety valve as in claim 22, further including means to couple said
safety valve to said primary gas valve and mating means incorporated into
said primary gas valve whereby said safety valve and said primary gas
valve can be seated together into said cylinder port.
37. A safety valve as in claim 36, wherein said coupling means consists of
a slot in said threaded housing of said safety valve and a mating prong
protruding from the bottom of said primary gas valve.
38. A safety valve as in claim 22, further including remote actuation means
to achieve the seating of said poppet in said poppet seat without the
deflection or severing of said primary gas valve.
39. A safety valve as in claim 38, wherein said remote actuation means
consist of the use of a fusible material in said tubular portion of said
threaded housing to receive said poppet and hold said poppet off of the
poppet seat and the heating of said fusible material to a temperature
above its melting point, whereby said fusible material fails under the
force exerted by said bias means and said poppet seats in said poppet
seat.
40. A safety valve as in claim 22, further including flow restriction means
to regulate the flow of compressed gas from said cylinder while allowing
the unimpeded filling of said cylinder.
41. A safety device as in claim 40, wherein said flow restriction means
consists of a flap with an aperture therein pivotally attached to said
cylindrical housing, such that cylinder pressure forces said flap against
said cylindrical housing covering said aperture in said cylindrical
housing and allowing gas flow only through said aperture in said flap,
while the pressure of gas filling the cylinder forces said flap away from
said cylindrical housing allowing for the unimpeded filling of said
cylinder.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a safety valve device for compressed gas
cylinders and, more particularly, to a stand-alone safety valve configured
to be seated in the port of a compressed gas cylinder, below and
independent of the conventional primary gas valve, for the purpose of
instantly shutting off gas flow in the event of mechanical deflection or
severance of the primary gas valve, or on command.
2. Description of the Related Art
Compressed gas cylinders are potentially lethal missiles if the primary gas
valve is severed or deflected so as to allow an uncontrolled release of
the stored gas. Destruction from a runaway gas cylinder can be
catastrophic in terms of human injury and property damage. An even more
deadly potential exists if the cylinder contains toxic or explosive gases.
Loss of life can result if these gases are accidentally released, whether
or not the cylinder becomes an uncontrolled missile.
Primary gas valves have been designed so as to incorporate a safety shutoff
device as part of a primary gas valve. In such devices, a secondary valve
is incorporated into the primary valve, and it is biased into a held open
position. At such time as the primary valve is severed, the secondary
valve is actuated, preventing the sudden escape of gas from the
high-pressure cylinder. Examples of prior art combination safety and
service valves are shown and described in U.S. Pat. Nos. 3,648,893,
4,077,422, and 4,562,852. The secondary valves described in these patents
include either a cylindrical plug which engages a flat seating surface, or
a ball which engages a ball chamber, to close the flow passage.
The safety valve described in U.S. Pat. No. 4,907,617, authored by one of
the inventors of the present invention, and having a common assignee,
provided another means by which a safety valve could be integrated into a
conventional primary valve. The safety valve portion of the primary valve
includes a poppet seat and a poppet held off the poppet seat by a
frangible element, which is held in compression by means of a helical
spring. A severing of the primary valve, or other structural disruption of
the valve, serves to break the frangible element, thereby seating the
poppet in the poppet seat and shutting off the flow of gas from the
cylinder. A unique advantageous feature of this safety valve is the use of
a frangible element to hold off the seating of the poppet. This is not to
say, however, that improvement of this earlier safety valve is not
possible and indeed the present invention constitutes an improvement of
the basic structure and characteristics of the safety valve described in
the above-identified patent.
More particularly, while the earlier safety valve included a frangible
element, the element will not break until the primary valve receives a
significant blow resulting in the severing, or major structural
distortion, of the primary valve. Therefore, it is desirable to provide a
safety valve which shuts off gas flow upon relatively small deflections of
the primary gas valve, or to shut off gas flow upon the command of the
operator in the event the primary gas valve has become inoperative or
ineffective due to leakage around the threads.
Further, the earlier safety valve must be mechanically integrated into the
body of a primary gas valve. The retrofitting of a primary gas valve is
difficult to perform and is met with disfavor by the manufacturers of
primary valves. Therefore, it is desirable to provide a safety valve which
could work cooperatively with conventional primary gas valves, but which
does not have to be mechanically integrated into or require modification
of the primary valve.
Even further, the earlier safety valve does not address the problem of gas
leakage past the threads of the primary valve where the primary valve
receives a blow resulting in damage to its threads. Blows to primary
valves often result in leakage of gas about the threads, which can be
extremely dangerous in the case of cylinders containing toxic or explosive
gases. Therefore, it is desirable to provide a safety valve which forms an
independent threaded seal with the cylinder, which will not be damaged in
the event that the primary valve experiences thread damage.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a safety valve for a
compressed gas cylinder which is an improvement over the earlier designs
by virtue of incorporating structures capable of providing the
advantageous functions noted above. In particular, in accordance with the
present invention, a safety valve is provided which will shut off gas flow
from a compressed gas cylinder upon relatively small deflections of the
primary gas valve.
Another object of the present invention is to provide a stand-alone safety
valve which works cooperatively with conventional primary gas valves and
conventional compressed gas cylinders.
It is a further object of the present invention to provide a safety valve
which does not require any modification to the primary gas valve.
Yet another object of the present invention is to provide a safety valve
which will form an independent threaded seal with the cylinder, one which
will not be damaged in the event that the primary valve experiences thread
damage.
Further, in accordance with the present invention, a flow restriction
device is provided to limit the flow of gas to a desired and
pre-determined rate and yet not interfere with filling operations of the
cylinder.
Yet another object of the present invention is to provide a safety valve
which allows for the remote triggering of the safety valve on command of
the user. In this manner, the safety valve can be triggered to stop the
flow of gas from a cylinder where a primary gas valve has become
inoperable due to corrosion or mechanical failure or where the primary
valve is leaking about its threads.
Other objects, features, and characteristics of the present invention, as
well as the methods of operation and functions of the related elements of
the structure, and the combination of parts and economies of manufacture,
will become more apparent upon consideration of the following description
and the appended claims with reference to the accompanying drawings, all
of which form a part of this specification, wherein like reference
numerals designate corresponding parts in the various figures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational perspective view of a safety valve provided in
accordance with the present invention, and showing how the safety valve is
used with a primary valve;
FIG. 2 is a broken-away front elevational view showing the valve provided
in accordance with the present invention inserted into a compressed gas
cylinder and located below and operating independently of but in
cooperation with a primary valve;
FIG. 3 is an exploded view of a first preferred embodiment of the valve
provided in accordance with the present invention;
FIG. 4 is a cross-sectional view of the valve of FIG. 3;
FIG. 5 is a plan view of a frangible ceramic pin provided in accordance
with the present invention displaying holes ablated by a laser beam;
FIG. 6 is a cross sectional view of the ceramic pin of FIG. 5 showing the
holes ablated by the laser beam;
FIG. 7 is an exploded view of a second preferred embodiment of the valve
provided in accordance with the present invention;
FIG. 8 is a cross-sectional view of the cylindrical housing of FIG. 7;
FIG. 9 is an exploded view of a third preferred embodiment of the valve
provided in accordance with the present invention;
FIG. 10 is a broken-away elevational view of the tubular portion of the
threaded housing of FIG. 9 showing the location of the spring pin;
FIG. 11 is a cross-sectional view of FIG. 10 showing a second view of the
location of the spring pin;
FIG. 12 is a perspective broken-away elevational view of the valve provided
in accordance with the present invention showing slots on the safety valve
which engage prongs on the primary valve;
FIG. 13 is a bottom plan view of the valve provided in accordance with the
present invention showing the addition of a flow restriction device; and
FIG. 14 is a broken-away elevational view of the threaded housing of FIG. 3
showing an alternative means for engaging the cone in said housing.
DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
An improved safety valve provided in accordance with the present invention
can be seen for example in FIGS. 1 and 2. The valve 10 is adapted for use
with a conventional compressed gas cylinder 12 of a type used to store
fluids at high pressures and with a conventional primary valve 14. The
primary valve is used to regulate the flow of a gas from the cylinder and
to provide a flow passage through which the cylinder may be filled, or
emptied. The safety valve 10 is a self-contained unit which works
independently of but cooperatively with the primary valve 14. It threads
into the cylinder port 16 in advance of the primary valve 14 and is
positioned below that threaded portion of the cylinder port occupied by
the primary valve. As can be best seen in FIG. 1, the threaded housing 18
of the safety valve is snugly received into the gas passage channel 20 of
the primary valve. During normal operation, gas from the compressed gas
cylinder flows through the inlet ports 22 of the cylindrical housing 24 of
the safety valve, through the threaded housing 18, and into the gas
channel 20 of the primary valve. The primary valve operates normally, and
the safety valve is invisible to the primary valve's function. Two-way gas
flow through the primary valve is minimally affected by the presence of
the safety valve. However, the presence of the safety valve protects
against release of gas in the event of severance or significant deflection
of the primary valve. If the primary valve is deflected as much as 10
degrees from vertical or if it is severed, the safety valve activates to
instantly shut off gas flow from the compressed gas cylinder.
Referring now to FIG. 3, the safety valve includes a cylindrical housing 24
and a threaded housing 18, which are attached together as more fully
described below. Apertures 22 are cut into the cylindrical housing to
allow for the passage of gas from the compressed gas cylinder through the
cylindrical housing, through the threaded housing, and into the gas
passage of the primary valve. The threaded housing 18 seats the safety
valve into the cylinder port 16. The threaded housing provides for a
poppet seat (not illustrated). A poppet 26 is biased into the poppet seat
by the helical spring 28. The poppet slidably travels on shaft 30 which is
centered within and held in place in the lower portion of cylindrical
housing 24 by means of flange 32. The flange is welded or otherwise
permanently attached to the lower end of cylindrical housing 24. The
helical spring 28 is positioned on shaft 34 to bias the poppet into the
poppet seat preventing the flow of gas to and from the cylinder. The
poppet 26 slidably travels within the cylindrical housing 24 by means of
guide 36, which is configured to allow the passage of gas around the
poppet. The tubular portion 44 of the threaded housing 18 contains a
frangible element 38 disposed longitudinally within the tube. One end of
the frangible element is snugly received in a channel 40 in poppet 26. The
other end of the frangible element is received into the cone 42. The cone
incorporates a number of gas passages to allow for the flow of gas through
the threaded housing and into the gas passage channel of the primary
valve. The cone is welded or permanently attached within the tubular
portion of the threaded housing. The cylindrical housing 24 is forced
inside the threaded housing 18, and the cylindrical housing is then welded
or permanently attached to the threaded housing completing the assembly of
the valve. This force places the frangible element into compression,
compresses the helical spring 28, and disposes the poppet away from the
poppet seat allowing for the free passage of gas through the safety valve.
The tubular portion 44 of the threaded housing 18 is sized so as to be
received snugly inside the gas passage 20 of the primary gas valve. The
inside diameter of the gas passage of the primary gas valve is consistent
among the various manufacturers of primary valves. However, minor
variations in diameter can be accommodated through the use of sleeves of
differing thickness to slip over the tubular portion of the threaded
housing and be snugly received into the gas passage of the primary valve.
A tightly fitting helical spring can also be slipped over the tubular
portion of the threaded housing to assist in achieving a tight fit. It is
desirable to achieve a snug mating of the threaded housing of the safety
valve and gas passage of the primary gas valve.
A collar 46 with inside and outside threads may be employed between the
threads of the safety valve and those of the cylinder port. Use of a
collar aids in the seating of the safety valve in the lower threads of the
cylinder port 16 and greatly reduces the risk of thread leakage at the
cylinder port in the event of damage to the primary valve. The collar is
made from a compliant material compatible with the gas service. For most
gases, such a material would ideally be a polymer material. A particularly
suitable material for the collar is Kel-F, which is a registered trademark
of 3M Corporation for a proprietary fluoroplastic. Kel-F is particularly
desirable as it is harder than most polymers, easily machined, and does
not cold-flow as readily as other similar polymers.
The use of collars of varying sizes can facilitate the use of a standard
safety valve in cylinder ports of slightly different tolerances, or the
placement of the valve at varying levels in the cylinder port. It has been
found that a standard size collar, and additional collars sized to be one
and one-half turns larger and smaller than the standard, will allow for
the correct fitting of the safety valve into virtually all cylinder ports.
Consistent with standards established by the Compressed Gas Association,
cylinder ports have tapered threads cut by taps. Of necessity, the lower
threads in the cylinder port are less precise than are the upper threads.
Use of a collar made from a polymer material facilitates the insertion of
the safety valve into the lower region of the cylinder port and ensures a
tight seal.
Thread leakage can be a significant problem for various kinds of gas
service. Often when a primary valve receives a blow or is more slowly
deflected from the vertical, thread damage occurs, resulting in a slow
leak through the threads of the primary valve and the cylinder port.
Thread leakage from compressed gas cylinders containing toxic or explosive
gases can be catastrophic in terms of human death, injury, and property
damage. Complicating the situation, thread leakage often is difficult to
determine until harm occurs. Use of the collar 46 with the safety valve
establishes an extremely tight seal below the threads of the primary
valve. Subsequent damage to the threads of the primary valve will not
result in a leak around the threads of the safety valve, as the blow or
deflection received by the primary valve is not transmitted to the safety
valve threads.
Referring now to FIG. 3, a washer 48 is employed in safety valves where it
is important to eliminate any possible gas leakage, such as in the case of
gas service involving toxic or explosive gases. The washer 48 is
compressed between the cylindrical housing 24 and the threaded housing 18.
A knife edge 50 is cut into the top rim of the cylindrical housing 24 and
a second knife edge (not shown) is cut into the portion of the threaded
housing 18 receiving the washer (not shown). Compression of the washer
between the mating knife edges minimizes leakage between the cylindrical
housing and the threaded housing. The center hole cut in the washer serves
as the poppet seat to receive the poppet. The washer is made from a
compliant material suitable for the gas service. For most gases, such a
material would ideally be a polymer material. As discussed above for the
collar 46, a particularly suitable material for the washer is Kel-F.
The safety valve of the present invention may be made of various materials
consistent with the gas service. A particularly appropriate material for
the valve is a stainless steel, such as 316 or 316L stainless steel, which
is corrosion-resistant and can be cleaned and electropolished. Alternative
materials for the valve include: brass; bronze; nickel alloys, such as
INCONEL; plastics, such as fiber resin plastic; and various polymers used
in valving. In cases where stainless steel cannot be used, such as with
fluorine gas, an aluminum-silicon-bronze alloy may be utilized.
The frangible element 38 of the present invention may also be made from
various materials and in various configurations. The material selected
should have a high ratio of compression and tensile strength to shear
strength and be compatible with the gas service. In one preferred
embodiment of the invention, the frangible element is a ceramic pin formed
of alumina (aluminum oxide), which is corrosion-resistant to many types of
gases. An alumina ceramic pin has high compression and tensile strength
and low shear strength. When relatively low bending and shear stresses are
applied to the pin, the pin will fracture.
It is desirable to be able to anticipate where the frangible element will
break by mechanically weakening the pin. In one embodiment of the
invention, the frangible pin 38 has a waist 52 cut round the pin to
establish a zone of decreased shear strength, inducing the pin to break in
this zone. In the alternative, if a ceramic frangible element is used, a
waist or other zone of decreased shear strength can be molded into the
ceramic material at the time the pin is formed, and before the material is
fired.
In another preferred embodiment, the frangible element may be weakened by
the use of a laser beam. As shown in FIGS. 5 and 6, an industrial laser
may be used to ablate a number of holes 54 into the circumference of a
frangible ceramic pin. In a preferred embodiment, an industrial laser is
used to ablate 10 to 20 spaced indentations into the ceramic pin with a
depth to width aspect ratio in the range of 5:1 to 1:1. The holes may be
made by turning the pin while the laser is held in a fixed position. The
pin can also be translated along the longitudinal axis of the pin while
the pin is turned before the laser. One cycle of translation to one cycle
of rotation will result in an elliptical pattern of holes in the pin as
shown in FIG. 5.
In use, then, a safety valve of the present invention is selected which is
constructed of materials compatible with the gas service. The tubular
portion 44 of the threaded housing 18 is checked to assure a snug fit into
the gas passage channel 20 of the primary valve being utilized. If
necessary, cylindrical shims or a helical spring may be utilized between
the tubular portion of the threaded housing and the gas passage channel of
the primary valve to ensure a snug fit. The position of the primary valve
in the cylinder port is identified, and the safety valve is screwed into
the cylinder port to a level immediately below the level to be occupied by
the primary valve. If the gas service involves toxic or explosive gases, a
collar 46 is utilized to prevent thread leakage. Spanner holes 56 and a
suitable spanner wrench (not illustrated) are utilized to seat the safety
valve at the appropriate level of the cylinder port. The primary valve is
then screwed into the cylinder port in its customary position.
The safety valve remains in the cylinder port throughout the service life
of the primary gas valve. The primary valve is operated normally and the
safety valve is invisible to the primary valve's function. In the event
that the primary valve receives a blow which severs the primary valve, or
a force which deflects the primary valve as much as 10 degrees from the
normal, the shear stress on the primary valve is transferred to the
tubular portion 44 of the threaded housing 18. This stress is thereby
further transferred to the frangible element 38. As the frangible element
is unable to withstand bending and shear stresses, it will break at its
weakest point. Upon the breaking of the frangible element, the helical
spring 28 will cause the poppet 26 to seat in the poppet seat, instantly
shutting off the gas flow from the compressed gas cylinder.
Once the safety valve has been actuated, the compressed gas cylinder will
remain in a safe condition until the cylinder can be emptied of its
contents. A cylinder containing a non-toxic or non-explosive gas can be
emptied by, first, securing the cylinder; second, removing the remaining
portion of the primary valve; and, third, performing a controlled bleeding
off of the gas in the cylinder. The controlled bleeding can be effected by
applying controlled pressure to the poppet 26 so as to force the poppet
off of the poppet seat. A tool or jig (not illustrated) may be utilized to
apply controlled pressure on the poppet. The same steps are used to empty
a cylinder containing a toxic or explosive gas. However, it is also
necessary to employ means to collect the gas leaving the cylinder and
prevent leakage to the atmosphere. A cylinder coffin and/or a gas
collection chamber may be utilized for this purpose.
Referring now to FIG. 7, a second preferred embodiment of an improved
safety valve provided in accordance with the present invention can be
seen. The safety valve has fewer parts, is less expensive to manufacture,
and is particularly suitable for use with non-toxic gas service. A
cylindrical housing 58 and a threaded housing 18 are attached together as
more fully described below. Referring to FIG. 8, apertures 60 are cut into
the bottom end of the cylindrical housing to allow for the passage of gas
from the compressed gas cylinder through the cylindrical housing, through
the threaded housing, and into the gas passage channel 20 of the primary
valve. The threaded housing 18 seats the valve into the cylinder port 16.
The housing provides for a poppet seat (not illustrated). A poppet 64 is
biased into the poppet seat by the helical spring 62. The poppet 64 is
machined from square stock of a size which can snugly, but slidably,
travel inside the cylindrical housing 58. The helical spring 62 is
positioned on shaft 66 to bias the poppet into the poppet seat preventing
the flow of gas to and from the compressed gas cylinder. The poppet 64
slidably travels within the cylindrical housing 58 guided by the edges of
the stock from which it is machined. Gas is allowed to pass along the
sides of the poppet. As was described in the first preferred embodiment,
the tubular portion 44 of the threaded housing 18 contains a frangible
element 38 disposed longitudinally within the tube. One end of the
frangible element is snugly received in a channel 68 in poppet 64. The
other end of the frangible element is received in a cone 42. The frangible
element 38 and cone 42 are illustrated by reference to FIG. 3. The cone
incorporates a number of gas passages to allow for the flow of gas through
the threaded housing and into the gas passage channel of the primary
valve. The cone is welded or permanently attached within the tubular
portion of the threaded housing. The cylindrical housing 58 is forced
inside the threaded housing 18, and the cylindrical housing is then welded
or permanently attached to the threaded housing completing the assembly of
the valve. This force places the frangible element into compression,
compresses the helical spring 62, and disposes the poppet 64 away from the
poppet seat allowing for the free passage of gas through the safety valve.
This safety valve has fewer parts, is less expensive to manufacture, and
is particularly suitable for use with non-toxic gas service such as
oxygen. However, it should be realized that the valve can also be modified
for use with toxic or explosive gases. In such service, a collar 46 and a
washer 48 compatible with the gas service would be added to the valve.
Referring now to FIG. 9, a third preferred embodiment of an improved safety
valve provided in accordance with the present invention can be seen. A
cylindrical housing 58 and a threaded housing 74 are attached together as
more fully described below. Referring to FIG. 8, apertures 60 are cut into
the bottom end of the cylindrical housing to allow for the passage of gas
from the compressed gas cylinder through the cylindrical housing, through
the threaded housing 74, and into the gas passage channel 20 of the
primary valve. The threaded housing 74 seats the valve into the cylinder
port 16. The housing provides for a poppet seat (not illustrated). A
poppet 70 passes through the poppet seat and is biased into the poppet
seat by the helical spring 62. The poppet 70 is machined from square stock
of a size which can snugly, but slidably, travel inside the cylindrical
housing 58. The helical spring 62 is positioned on shaft 72 to bias the
poppet into the poppet seat preventing the flow of gas to and from the
compressed gas cylinder. The poppet 70 slidably travels within the
cylindrical housing 58 guided by the edges of the stock from which it is
machined. Gas to and from the compressed gas cylinder passes along the
sides of the poppet. A frangible tube 76 is connected to the threaded
housing 74 through a mechanical connection. Such a connection can be
achieved by adding to one end of the tube an outwardly flairing rim to
retain the tube inside the threaded housing. Alternatively, a mechanical
connection can be achieved through the heat shrinking of dissimilar
materials or the use of adhesives. The frangible tube 76 is made from a
frangible material, similar to the materials used for the ceramic pin 38
and discussed above. Two holes 78 are drilled through the frangible tube
76 at approximately one-half inch up from the bottom of the frangible tube
76. A suitably sized spring pin 80 is inserted through the holes. The
poppet 70 is disposed against the poppet seat in the housing 74 by the
helical spring 62, which slides on the lower shaft of the poppet 70 and is
opposed by the bottom plate of the cylindrical housing 58. The poppet
includes a stem 82 which is disposed against the spring pin so as to
normally hold the poppet in an open position away from the poppet seat.
The cylindrical housing 58 is forced inside the threaded housing 74, and
the cylindrical housing is then welded or permanently attached to the
threaded housing completing the assembly of the valve.
At such time as the primary valve receives a blow or is deflected, the
bending force is transferred to the frangible tube 76. A sufficient
bending moment applied to the frangible tube results in a breaking of the
tube which allows the poppet 70 to seat in the poppet seat. A bending
force applied to the frangible tube 76 will result in a breaking of the
tube at its weakest point, which is at the point where the holes 78 are
drilled.
Referring again to FIG. 9, it is very desirable that a waist 84 be cut into
the frangible tube 76 below the spring pin 80 to induce breaking of the
tube at the waist, rather than at the holes 78. In this embodiment, the
poppet 70 is held in a long-term stable condition off of the poppet seat
by the frangible tube 76 held in compression. However, at such time as the
frangible tube breaks at the waist 84, the portion of the frangible tube
above the waist is pushed away by the poppet 70, as the poppet is forced
into the poppet seat by the helical spring 62, and the separated portion
of the frangible tube poses no possible obstruction to the seating of the
poppet 70.
Some materials selected for the frangible tube may be difficult to drill.
For such materials, it may be desirable to grind narrow, horizontal slots
circumferentially into the frangible tube. In such an application, the use
of a spring pin is discouraged. Instead, a slab of material, such as shim
stock compatible with the gas service, may be slipped through two of such
slots and provide a bridge to hold the poppet off of the poppet seat. As
the use of slots results in significant weakening of the tube, there is no
need to additionally weaken the frangible tube through the use of a waist.
Referring now to FIG. 12, an alternative means to seat an improved safety
valve provided in accordance with the present invention can be seen. Slots
86 are cut into the top surface of the threaded housing 18 so as to mate
with corresponding prongs 88 on the bottom face of a primary gas valve 14.
The tubular portion 44 of the threaded housing 18 is first inserted into
the gas passage channel 20 of the primary gas valve 14. Next, prongs 88 of
the primary gas valve are mated with the slots 86 of the safety valve.
Finally, the safety valve and the primary gas valve are seated as a unit
into the cylinder port of a compressed gas cylinder.
Referring now to FIG. 13, a means to incorporate a flow restriction device
into the improved safety valve provided in accordance with the present
invention can be seen. Flow restriction orifices on primary gas valves are
in common use in many industries, including the electronics industry,
particularly with toxic gases. However, such devices must be removed prior
to filling the compressed gas cylinder, and they are exposed to ambient
conditions, resulting in corrosion of the device and the degradation of
its utility. These problems are solved by the present invention. A flap 90
is shown, attached to the bottom of cylindrical housing 58, as shown in
FIGS. 7 and 8. The flap 90 is constructed out of a pliant material
compatible with the gas service, such as stainless steel shim stock. The
flap includes a restrictive orifice 92 to limit the flow of gas from the
compressed gas cylinder to the primary gas valve, sized for the desired
delivery of gas. One side of the flap is spot welded 94 or otherwise
permanently attached to the bottom of the cylindrical housing 58. The
remaining three sides are unattached, allowing the flap to move away from
the bottom of the cylindrical housing when under filling pressure.
In use, then, compressed gas inside the cylinder forces the flap 90 against
the bottom of cylindrical housing 58, shutting off the flow of gas through
holes 60. The flow of gas from the compressed gas cylinder is thereby
restricted to the flow though the orifice in the flap, which is sized
consistent with the desired flow from the primary gas valve. When the
compressed gas cylinder is filled, supply gas is forced in the opposite
direction through cylindrical housing 58 and holes 60. The pressurized
flow of gas passing through holes 60 will push the flap 60 away from the
bottom of cylindrical housing 58, allowing the cylinder to be filled in an
unrestricted manner without the flow constraint imposed by the orifice.
Referring finally to FIG. 14, a means to remotely trigger the improved
safety valve provided in accordance with the present invention can be
seen. It is desirable to shut off the flow of gas from a pressurized
cylinder to a primary gas valve in cases where the primary gas valve has
become inoperable through corrosion or mechanical failure. A particularly
dangerous situation arises where a malfunctioning primary gas valve
refuses to adjust or close off the flow of gas for toxic or explosive gas
service. Such a dangerous condition can be alleviated by the present
invention. A cone 42 is shown configured to be received inside the tubular
portion 44 of the threaded housing, as more fully illustrated by reference
to FIG. 3. However, in the present embodiment, the cone 42 is retained
inside the tubular portion of the threaded housing by means of a shoulder
43 incorporated into the rim of the tube. The cone is fabricated out of a
fusible or eutectic material which will soften or melt at a pre-determined
temperature, or range of temperatures, and which is compatible with the
gas service.
Particularly suitable materials for the cone are alloys employed in
conventional fusible plugs which are employed in overpressure safety
devices utilized on many primary gas valves. Two alloy materials are
commonly used in such applications. The metal alloy used in Type CG-2
fusible plugs melts at approximately 165 degrees F., and the alloy in Type
CG-3 fusible plugs melts at approximately 212 degrees F. In fashioning the
cone, the metal alloy can be plated or coated so as to be inert to the
intended gas service. Depending on the service, platings of gold,
platinum, or other metals may be suitable. In other service, the cone may
be coated with Teflon or polymer coatings.
In use, then, a malfunctioning primary gas valve is heated by means of a
torch or a resistive heating element, and the heat is applied to the
portion of the primary gas valve in contact with the tubular portion of
the threaded housing and cone of the safety valve. At such time as the
cone is heated above its pre-determined melting temperature, it yields and
no longer affords resistance to the force exerted on the frangible element
38, and the poppet 26, by the helical spring 28, and the poppet engages
the poppet seat thereby closing off the flow of gas from the compressed
gas cylinder. Once the poppet has seated in the poppet seat, the primary
gas valve can be removed by conventional means.
U.S. Department of Transportation (DOT) regulations generally require the
use of overpressure safety devices on primary gas valves, except for toxic
gas service. Such devices employ a fusible plug, a burst disk, or both. As
has been explained, the safety valve of the present invention can under
certain circumstances shut off the flow of compressed gas to the primary
gas valve and thereby interfere with the operation of an overpressure
safety device. The DOT has not ruled whether the safety valve of the
present invention can be utilized with gas service requiring the use of
overpressure safety devices on primary gas valves. An alternative solution
would be a redesign of the safety valve to incorporate an overpressure
safety device into the safety valve. Such a modification would integrate a
gas passage through the poppet to provide a means for the flow of gas from
the compressed gas cylinder to the primary gas valve after the safety
valve was triggered the poppet was seated in the poppet seat. On the
downstream side of the gas passage through the poppet would be mounted an
overpressure device of a conventional design.
While the invention has been described in connection with what is presently
considered to be the most practical and preferred embodiments, it is to be
understood that the invention is not be to be limited to the disclosed
embodiment, but on the contrary is intended to cover various modifications
and equivalent arrangements included within the spirit and scope of the
appended claims.
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